Field
The present disclosure generally relates to methods and apparatuses for processing a substrate, and more specifically to methods and apparatuses for controlling photoresist line edge/width roughness.
Description of the Related Art
Integrated circuits have evolved into complex devices that can include millions of components (e.g., transistors, capacitors and resistors) on a single chip. Photolithography may be used to form components on a chip. Generally the process of photolithography involves a few basic stages. Initially, a photoresist layer is formed on a substrate. The photoresist layer may be formed by, for example, spin-coating. A chemically amplified photoresist may include a resist resin and a photoacid generator. The photoacid generator, upon exposure to electromagnetic radiation in the subsequent exposure stage, alters the solubility of the photoresist in the development process. The electromagnetic radiation may have any suitable wavelength, such as a wavelength in the extreme ultra violet region. The electromagnetic radiation may be from any suitable source, such as, for example, a 193 nm ArF laser, an electron beam, an ion beam, or other source. Excess solvent may then be removed in a pre-exposure bake process.
In an exposure stage, a photomask or reticle may be used to selectively expose certain regions of a photoresist layer disposed on the substrate to electromagnetic radiation. Other exposure methods may be maskless exposure methods. Exposure to light may decompose the photoacid generator, which generates acid and results in a latent acid image (defined at least in part by “latent image lines”) in the resist resin. After exposure, the substrate may be heated in a post-exposure bake process. During the post-exposure bake process, the acid generated by the photoacid generator reacts with the resist resin in the photoresist layer, changing the solubility of the resist of the photoresist layer during the subsequent development process.
After the post-exposure bake, the substrate, and, particularly, the photoresist layer may be developed and rinsed. After development and rinsing, a patterned photoresist layer is then formed on the substrate, as shown in FIG. 1. FIG. 1 depicts an exemplary top sectional view of the substrate 100 having the patterned photoresist layer 104 disposed on a target material 102 to be etched. Openings 106 are defined between the patterned photoresist layer 104, after the development and rinse processes, exposing the underlying target material 102 for etching to transfer features onto the target material 102. However, inaccurate control or low resolution of the lithography exposure process may result in the photoresist layer 104 having being formed with undesirable dimensions, such as unacceptable line width roughness (LWR) 108. Furthermore, during the exposure process, acid generated from the photoacid generator may diffuse randomly, including into regions under the mask where such acid is not intended to be diffused. This unintended diffusion may create undesired wiggling and/or an undesired roughness profile 150 at the interface of the patterned photoresist layer 104 with the openings 106. Large line width roughness (LWR) 108 and undesired wiggling profile 150 of the photoresist layer 104 may result in inaccurate feature transfer to the target material 102, which may lead to device failure and/or yield loss.
Therefore, there is a need for a method and an apparatus to control line width roughness (LWR) so as to obtain a patterned photoresist layer with desired dimensions. There is also a need for a method and an apparatus to control and reduce line edge/width roughness.